The temperature of a liquid cooled internal combustion engine can be modulated by a liquid coolant circulated through the engine and a radiator. There are sophisticated built-in systems for controlling the temperature of the liquid coolant by controlling the rate at which it circulates. Under extreme conditions, however, the liquid coolant may still be too cold or get too hot. If the coolant is too cold, the engine may run rough or stall and if the coolant is too hot, the engine may overheat and be damaged. Overheating can occur when the motor vehicle is driven hard or in heavy traffic necessitating frequent stops and starts. If the vehicle has air conditioning, the air conditioner is frequently driven by the engine and this additional load causes further overheating. Overcooling can occur under extremely cold driving conditions.
A liquid cooled engine can be cooled by running the heater in the passenger compartment. This works because the heat given off by the heater comes from the coolant, a portion of which is routed through a heater core for warming the passenger compartment. This technique, while effective at reducing the temperature of the circulating liquid coolant in hot weather, is at the expense of the passengers' comfort. Other than for running the heater, there is no simple way for the operator of the vehicle to affect the temperature of the liquid coolant.
There are various add-on systems for heating or cooling a liquid cooled engine. For example, there are electrical heaters for heating the coolant and evaporators for cooling the radiator. There is a system for directing a side stream of air from an air conditioner onto the radiator and another system for directing a stream of heated or cooled air from an auxiliary air tempering unit onto the radiator. None of these systems, however, make use of conventional heating/cooling systems normally found on motor vehicles as the basis for an auxiliary system for heating and cooling the liquid coolant.